Method for determining proper color balance in color printing base

ABSTRACT

A step-wedge is reprinted four times, one for each of three colors plus black and white as a mask. The reprinting is in a different position each time, giving a total of four different positions with one selected value overprinted by each color to show the effect of the overprint, namely to demonstrate a neutral. If a neutral gray is obtained, then it is known that the printing is correct. If no neutral is obtained, a ready reference, not requiring the use of a densitometer or separation filters is immediately at hand.

United States Patent inventor Joseph J. Smaio Chicago, Ill.

App]. No. 845,288

Filed July 28, 1969 Patented Nov. 16, 1971 Assignee Opto/Graphics, Inc.

Kenilworth, lll.

METHOD FOR DETERMINING PROPER COLOR BALANCE 1N COLOR PRINTING BASE 4 Claims, 7 Drawing Figs.

US. Cl

Int. Cl

Field of Search 96/27 E, 356/1 75 G03c 5 04, G01 j 3/46 ..96/23, 27 E,

[56] References Cited UNITED STATES PATENTS 2,446,111 7/1948 Simmon et al. 96/23 X 2,446,112 7/1948 Simmon et al. 96/23 X 2,450,307 9/l948 Simmon et al. 96/23 X 3,285,125 11/1966 Mitchell 96/27 X Primary ExaminerNorman G. Torchin Assistant Examiner-Alfonso T. Suro Pico Attorney-Olson, Trexler, Wolters & Bushnell ABSTRACT: A step-wedge is reprinted four times, one for each of three colors plus black and white as a mask. The reprinting is in a different position each time, giving a total of four difierent positions with one selected value overprinted by each color to show the effect of the overprint, namely to demonstrate a neutral. If a neutral gray is obtained, then it is known that the printing is correct. if no neutral is obtained, a ready reference, not requiring the use of a densitometer or separation filters is immediately at hand.

44 54a 42 see,

we ar f 7 e egg; 0 8 6 09%) 5 O afiz/vflms) U 0 0 g 0 (MAGENm) L/mt) D WWWM 0 O O I O O O O 0 5 .54 5Q M1 40 5 d O o I o o o o o o o 10 METHOD FOR DETERMINING PROPER COLOR BALANCE IN COLOR PRINTING BASE BACKGROUND OF THE INVENTION Tricolor printing process of various types are known in the art. In order to balance the three colors it is common practice to provide a photographic step-wedge or step tablet, comprising a graduated exposure index, which is reprinted on itself. With the aid of a densitometer a skilled operator can study the overprinted step-wedge, and determine whether the color balance is proper, or whether it is necessary to add or subtract one or more colors. This is time consuming and requires a skilled operator, and is hence quite expensive.

SUMMARY OF THE INVENTION A step-wedge is provided with images more or less in the shape of an offcenter T. Four square or other geometric areas run from nearly clear through dark gray, and form the crossbar of the T. The stem of the T underlies the third area, thereby being somewhat offcenter, and comprises two squares or other geometric areas, the most remote one relative to the crossbar duplicating one of the aforementioned gray areas of the crossbar, and the immediate area being black (opaque). An easel or base is provided with pins, and the exposure index is successively positioned in four different positions, relatively rotating about the most remote geometric area of the stem, whereby this area is overprinted in three different colors plus black and white. If this particular area ends in a neutral gray, then it is known that the color balance is correct. If it has a hue of one color, it is known that this color must be reduced, or one of the others intensified, and the intensities of the other areas covered in indifferent colors indicate relative intensities of the colors readily without requiring a densitometer or a skilled operator, thereby greatly facilitating color correction.

Accordingly, it is an object of the present invention to provide an improved target or exposure index having a novel stepwedge thereon which is overprinted in each of the printing colors with one gray area being overlapping in each instance to provide an indication of color balance.

It is likewise an object of the present invention to provide a novel step-wedge and method of using the same which does not require a densitometer or a skilled operator.

Other and further objects of the present invention will be apparent, and the invention will be readily understood from the following description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 comprises a perspective view of the graduated index of target;

FIG. 2 comprises a perspective view of the easel usable therewith and having a sheet of paper thereon;

FIG. 3 is a view showing the position of exposure for the magenta print;

FIG. 4 is a similar view showing the position of exposure for the black and white print;

FIG. 5 is a similar view showing the position of exposure for the yellow print;

FIG. 6 is a similar view showing the position of exposure for the cyan print; and

FIG. 7 is a similar view showing the multicolor print as actually made.

Turning now in greater particularity to the drawing, and first to FIG. 1, there will be seen a test device or target I0 constructed in accordance with the present invention. This device includes a clear sheet base 12, constructed of suitable material such as cellulose acetate. The base is provided with four ruled margins 14, l6, l8, and 20, respectively, and individually labeled as to first, second, third, and fourth position.

Each margin is provided with three keyed holes, the holes in the first margin being identified as 22, 24 and 26. The like holes in the subsequent margins are identified by similar numerals with the respective addition of suffixes a, b, and c. In addition, the target base is provided with a step-wedge identified generally by the numeral 28.

The step-wedge is generally in the shape of a slightly offcenter T. The crossbar of the T comprises four aligned squares, 30, 32, 34 and 36. The stem of the T is aligned with the square 34, and includes additional squares 38 and 40. It is to be understood that the square shape is arbitrary, and that other geometric shapes could be used. However, a square shaped is easy to make, and fits other requirements, as will appear hereinafter. The first square (or patch) 30 is very nearly clear, but preferably has a 0.05 defuse optical density to separate the image formed thereby from the background. The adjacent three patches, 32, 34, and 36 are logarithmically related to one another. The patch 38 is opaque, having density of 2.0 or higher, while the center patch 40 has a density of 0.30 although this value is not critical. The center square 40 is the same optical density of one of the other squares or patches, and in the illustrative example it is the same as patch 36.

Turning now to FIG. 2, I also provide an easel 42. Since the present invention is practiced with particular utility in electrostatic printing the easel is preferably metal and is grounded. The paper can be charged direct on an easel to avoid undue handling of the paper. The easel is provided with three up standing pins 44, 46, and 48 respectively mating with the holes 22, 24, and 26 in the margin of the target. (It will be understood that the pins also subsequently mate with the like numbered holes with the respective sufiixes a, b, and c. A sheet of printing paper 50 having holes along only one edge designed to mate with the pins 44, 46, and 48 is placed on the easel with the holes receiving the pins, as seen in FIG. 2. The final printed paper 50 is sown in FIG, 7, the pin receiving holes being identified at 52, 54, and 56. In accordance with the first example of the present invention, the paper is coated with a zinc oxide and resin formulation so that the paper can be elec trically charged in accordance with known techniques, preferably direct on the easel 42, but optionally elsewhere. The target is likewise placed on the easel, overlying the paper 50, and first in the first position as shown in FIGS. 2 and 3.

As will be understood in this first position the holes 22, 24 and 26 are centered on the pins 44, 46, and 48. Light is projected through the target 10 onto the paper 50 through a green filter. Subsequent to the exposure the the target is removed. and the paper is processed in a liquid toner containing magenta dye whereby a positive magenta image of the step-wedge is produced on the paper. Preferably only the surface of the paper is wet during the processing, as in accordance with the application of Meyer L. Sugarman and Joseph H. Jaeger, Ser. No. 692,234, filed Dec. 20, 1967 recently refiled as two divisional applications, Ser. No. 859,219, filed July I l, 1969, (case IA), and Ser. No. 841,097 filed July ll, 1969, (case 1B).

After drying of the paper, should this step be necessary if the toning is carried out by an immersion process, the paper is returned in the same position to the easel. However, in this instance the target is placed in the second position with the holes 220, 24a, and 26a positioned over the pins 44, 46, and 48 respectively. As will be understood, the paper is charged before the target is positioned over it. Exposure then is made by means of white light with no filter, and development is in black and white to produce a positive black and white image. It will be noted that the gray patch 40 is in identically the same position in FIGS. 3 and 4, although turned 90, the remainder of the step-wedge pattern being turned 90", likewise.

Following toning of the paper in black and white, it is returned to the easel in the same position, being charged on the easel, or before hand. The target then is placed over thpaper in the third position, as shown in FIG. 5, the holes 22b respectively overlying the pins 44, 46, and 48. As will be ob served, the target is in l inverted position relative to the first position with the center gray patch 40 again being precisely positioned over its previous positions. In the third position exposure is through a blue filter, and the image is toned in a toner containing a yellow dye, whereby to provide a yellow positive image of the step-wedge.

Following toning the paper is again returned to the easel in a dry condition, and is charged thereon, or before hand. The target is placed over the paper in the fourth position with the holes22c, 24c, and 26c respectively the pins 44, 46, and 48. The paper is then exposed through the target and through a red filter, toning subsequently being done in a positive toner containing cyan dye.

The final print of FIG. 7 will have a row of magenta squares of varying intensities across the top, a row of gray squares along the left, a row of yellow squares along the bottom, and a row of cyan squares along the right. The adjacent square 38 in each instance will be of the same hue as the adjacent row. Finally, the center square 40 comprises all three colors (plus black) printed in proper relative intensities, then this center square 40 will bea neutral gray. If it is shaded with one of the three hues, or two thereof, it is known immediately that the relative intensity of that particular hue (or hues) is too great, and that a subsequent test print should be made giving a shorter exposure with the complementary light color to that hue (or hues). Meanwhile the three rows of different color hues and the three squares immediately adjacent the center square of different hues give a ready indication of the relative intensities of the three hues, thereby making an estimate on the part of the operator as to the additional printing time to be added or subtracted for any one given hue a relative simple matter requiring no densitometer and requiring only a minimum of experience. As will be understood, the gray row and adjacent square are provided to give an indication of the degree of masking.

As will be apparent, l have now disclosed and improved step tablet or step-wedge and a method of using the same to make a color test print providing a ready reference which does not require the use of a densitometer or separation filters. The relative strength of each component color can be seen immediately, whereby the operator or printer can quickly made a judgment as to the degree of correction needed and to what extent the correction should be made.

The invention has particular utility to electrostatic printing, due to the ability to lay down one color at a time, and due to the speed of operation. With respect to the latter, printing times for the various times run on the order from several seconds to a few minutes, while toning or printing times runs only a matter of seconds with drying time to be negligible when toning is handled with only the face of the paper being exposed to the toner, as in accordance with aforesaid copending application referred hereinto.

Since the colors are printed, it is essential that the toners already laid down not accept any electrostatic charge themselves, although the area under each toner will still accept the charge. It has been found that certain yellow toners do tend to accept charge, ans such yellow toners are still usable provided that the yellow toned print is made last.

Although reference has been made by way of example to electrostatically printing, it will be understood that the principles of the invention are applicable to any tricolor printing. For contact prints, substantially any light source can be used for making the exposure. However, it is convenient to use a photographic enlarger as the light source, inasmuch this is readily adaptable in projection prints as well as contact prints, it being understood that a small step-wedge would be used for making a projection test print.

The invention is claimed as follows:

1. The process of producing a color test print which comprises positioning a target having a pellucid base and a plurality of patches thereon of different densities in a predetermined position relative to the test printing base, exposing the test printing base through said target by means of light of one hue and subsequently developing said printing base to a complementary hue, moving said target to another position with one of said patches overlapping and exposing said printing base through said target to light of another hue and developing said base to a color complementary thereto, and moving said target to yet another position relative to said printing base with same patch again overlapping and exposlng to light of yet another UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,620,727 Dated November 16, 1971 Inventor(s) Joseph J. Smajo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 34 change "indilfferent' to --different-- Col. 1, line 49, after "graduated" insert --exposure-- Col. 3, line 4, after "respectively" insert -receiving-- Col. 3 line 14, after "printed in" insert --a single area. If

the three colors have been printed in-- C01. 3, line 35, change "made" to --make-- Col. line 5, after "printed" insert -sequentially-- Col. 4, line 38, change "claim 3" to --claim l-- Signed and sealed this 5th day of September 1972.

(SEAL) Attest:

EDWARD M. FLETCHER ,JR. ROBERT GOTTSCHALK Attest ing Officer Commissioner of Patents M F o-10 C! uscomm oc 50375-959 

2. The process as set forth in claim 1 which includes the further step of positioning the target in a fourth position relative to said printing base with the same patch overlapping, exposing to white light, and developing in black and white.
 3. The process as set forth in claim 3 wherein the target is rotated from one position to another.
 4. The process as set forth in claim 3 wherein the target is rotated about said one patch as a center. 